Imaging elements generally comprise a support, adhesion or tie layers (subbing layers), image recording layers, and auxiliary layers that serve other functions, such as scratch resistance, static abatement, magnetic recording or lubrication. U.S. Pat. No. 6,037,108, titled "THERMALLY STABLE SUBBING LAYER FOR IMAGING ELEMENTS," J. Chen, et al., filed Apr. 27, 1998, discusses the severe requirements for adhesion to the support and between layers in the imaging element. The inert character of most surfaces such as polyester surfaces presents considerable challenge for adhesion of layers coated thereon. As discussed in U.S. Pat. No. 6,037,108, J. Chen, et al., the adhesion difficulties have traditionally been overcome by the use of subbing systems involving etch agents as disclosed in U.S. Pat. No. 3,143,421, titled "ADHERING PHOTOGRAPHIC SUBBING LAYERS TO POLYESTER FILM," by G. Nadeau, et al., Aug. 4, 1964; U.S. Pat. No. 3,201,249, titled "COMPOSITE FILM ELEMENT AND COMPOSITION THEREFOR INCLUDING ANTI-HALATION MATERIAL," by G. Pierce, et al., Aug. 17, 1965, and U.S. Pat. No. 3,501,301, titled "COATING COMPOSITIONS FOR POLYESTER SHEETING AND POLYESTER SHEETING COATED THEREWITH," by G. Nadeau, et al., Mar. 17, 1970, or alternatively, by energetic treatments, including corona discharge, glow discharge (see for example U.S. Pat. No. 5,425,980, titled "USE OF GLOW DISCHARGE TREATMENT TO PROMOTE ADHESION OF AQUEOUS COATS TO SUBSTRATE," by J. Grace et al., Jun. 20, 1995, and references cited therein), ultraviolet radiation, electron beam, and flame treatment. Whether the support is treated by coating with a polymeric subbing layer containing an etchant or whether it is modified by energetic treatment, in many instances an additional subbing layer comprised of gelatin, or a single mixed subbing layer including a non-gelatin polymer and gelatin may be used. These gelatin and mixed subbing layers provide good adhesion to subsequently coated layers comprising hydrophilic colloid binders.
It is also mentioned in U.S. Pat. No. 6,037,108, that recently introduced systems such as the Advanced Photo System.TM. (APS) require thermal processing of the polyester support. The thermal processing is required in order to meet the mechanical specifications associated with the use of small format film in small cartridges, as well as the film loading and unloading mechanisms employed by APS cameras and APS film processors. The thermal treatment sufficiently reduces the core-set curling tendency of the polymeric film such that the mechanical requirements for the system are met. It is also stated that there are possible manufacturing benefits of coating the subbing layers prior to the requisite heat treatment. However, as disclosed in the above mentioned application, extended heat treatment or annealing processes applied to polyesters with gelatin or mixed subbing layers have been found to severely compromise the adhesion of subsequently coated hydrophilic colloid layers, such as silver halide emulsion layers of silver halide photographic elements.
The thermal degradation of the gelatin-containing subbing may result from thermally driven decomposition of the underlying support and subbing layer(s) and interaction of the byproducts with the gelatin subbing layer. In the case of a single mixed subbing layer, it may result from thermally driven chemical processes involving the non-gelatin polymer and gelatin. Hence, it may be desirable to have a single subbing layer that is both thermally stable and does not contain gelatin.
U.S. Pat. No. 5,563,029, titled "MOLECULAR GRAFTING TO ENERGETICALLY TREATED POLYESTERS TO PROMOTE ADHESION OF GELATIN-CONTAINING LAYERS," by J. Grace et al., Apr. 3, 1995, discloses the use of amine reactive hardeners in combination with nitrogen glow-discharge treatment (or some other means of producing surface amines) applied to polyester support to provide the adhesion function of the subbing system. Grace et al. show that bis(vinylsulfonyl)methane, a representative amine reactive hardener, can be used as a molecular primer to bond a gelatin-containing layer to a plasma-treated support. It is taught that the amine reactive hardener chemically bonds to the plasma-treated support and that the gelatin then bonds to the amine reactive hardener. Similar to its function as a cross linking agent, the hardener links the gelatin to the treated surface by covalent bonds that are established by reaction of the vinylsulfone groups in the hardner with amine groups in the nitrogen-plasma-treated surface and in the gelatin coating. Grace et al. does not suggest that amine reactive hardeners in combination with appropriate surface treatment (e.g., glow discharge) provide a thermally stable subbing layer. In fact, one skilled in the art would likely expect that the highly reactive hardeners disclosed by Grace et al. would undergo undesirable chemical reactions under prolonged exposure to heat (e.g., as required for the manufacture of film base for Advanced Photo System.TM. film).